1. Field of the Invention
The present invention relates to wireless keyboards for use in a data processing system and, more specifically, to antenna systems for wireless keyboards for use in a data processing system.
2. Description of the Related Art
Wireless keyboards for use with personal computers are known. Specifically, wireless infrared keyboards for use with personal computers are known. An infrared wireless keyboard simply uses an infrared transmitter in the keyboard and an infrared receiver in a personal computer to establish an input link from the keyboard to the personal computer. The wireless infrared keyboard does not, of course, need a physical wire connection between the keyboard and the personal computer so that there is no wire clutter.
The infra-red wireless keyboard, however, has numerous drawbacks. Specifically, the infrared wireless keyboard requires a clear line-of-sight between the infrared transmitter in the keyboard and the infra-red receiver in the personal computer. Moreover, the distance between the infrared keyboard and the personal computer must not be too great so that the infrared receiver in the personal computer cannot detect the infrared beam from the infrared transmitter of the wireless keyboard.
The clear line-of-sight and distance requirements constrain the flexibility a that user would desire with regard to a wireless device because an artificial limit is placed on the location and the distance that can exist between the infrared wireless keyboard and the personal computer. In addition, the infrared wireless keyboard has large power consumption requirements because of the infrared transmitter. The infrared wireless keyboard typically operates on a six-volt power source that is commonly derived from four 1.5-volt batteries. Moreover, the increased power consumption reduces overall battery life so that the batteries must be replaced more often.
Conventional radio-frequency (xe2x80x9cRFxe2x80x9d) wireless keyboards addressed some of the shortcomings of the infrared wireless keyboards. Conventional RF wireless keyboards required less power than infrared wireless keyboard, and therefore, provided greater overall battery life so that batteries were replaced less often.
Conventional RF wireless keyboards had drawbacks. One drawback is that the requirement of an RF antenna being large enough so that it is efficient in transmitting RF signals. For example, a conventional RF antenna using electromagnetic propagation principles has a RF antenna that is of the same order of size as the RF wavelength. For example, a 27 MHz signal has a wavelength of eleven meters and would require an antenna of approximately three to six meters for signal transmission. Such a large RF antenna, however, is incompatible with devices such as the wireless keyboard that must be small enough to remain convenient and handy.
To accommodate the requirement of a large antenna without frustrating the advantages of the convenience and handiness of a wireless keyboard, complex and expensive antenna circuitry is incorporated into the conventional RF wireless keyboard. Such circuitry, however, increase the production costs associated with the conventional RF wireless keyboard. Further, the complex and expensive circuitry also increases the power consumption by the system, and therefore, reduces the battery life so that the batteries are replaced more often. Moreover, in some instances even the complex and expensive antenna circuitry still lacks the efficiency for transmitting RF signals that a large RF antenna provided.
Therefore, there is a need for an antenna system for a wireless keyboard that (1) has operational flexibility without physical restraints on communication between the wireless keyboard and a personal computer, (2) is inexpensive to operate and produce without complex and expensive added circuitry, (3) is compact enough to reside within a small housing, (4) consumes less power, and (5) is relatively easy to realize.
The present invention includes a low-cost, efficient, compact antenna system for use in a wireless keyboard. The wireless keyboard includes a housing and keys. The antenna system includes a radio-frequency antenna for use in a radio-frequency wireless keyboard. The radio frequency (xe2x80x9cRFxe2x80x9d) antenna remotely couples the wireless keyboard to a personal computer or other device capable of receiving input from a keyboard.
The antenna system of the radio-frequency wireless keyboard includes an antenna wire having a first end and a second end, an RF printed circuit board that includes a digital processing circuit and a RF transmitter circuit, and a metallic plate having a first end and a second end within the wireless keyboard. In one embodiment, the printed circuit board may include a ground portion. The antenna system resides within the housing of the wireless keyboard.
The first end of the metallic plate is coupled to the an output of the RF transmitter circuit, which in one embodiment may be coupled to the ground portion. The second end of the metallic plate is coupled to the first end of the antenna wire. The second end of the antenna wire is coupled to another output of the RF transmitter circuit. Thus, the structure of the present invention forms an antenna loop that includes the antenna wire and the metallic plate as a component of the antenna loop. The antenna loop is used to generate a magnetic field from which RF signals are transmitted in accordance with electromagnetic propagation principles.
The RF printed circuit board includes a digital processing circuit and a RF transmitter for the radio frequency wireless keyboard. The metallic plate within the keyboard may be a metallic plate that is preexistent within a housing of a conventional keyboard. The metallic plate in the keyboard protects against electrostatic discharge. The metallic plate also creates a more rigid keyboard structure and adds some weight to the keyboard to generate a feeling of quality and durability with a user.
The antenna loop of the present invention has a length approximately equal to the length of the keyboard and a width that is as large as the remaining free space (height, length, and/or width) within the keyboard. Moreover, the antenna system is designed so that the entire antenna loop may be located within the housing of a conventional keyboard.
In an alternative embodiment, the RF antenna of the antenna system may be comprised of the metallic plate. For example, in one embodiment the antenna wire may be substituted with a cut-out of the metallic plate. The antenna system includes a metallic plate with a first portion and a second portion and a cut-out space in-between. The first portion is coupled to an output of the RF transmitter circuit and the second portion may be coupled to another output of the RF transmitter circuit or a ground. An antenna loop is formed by the first and the second portions and the length of the antenna loop is the length of the keyboard while the width of the antenna is as large as the remaining free space (height, length, and/or width) of the keyboard. Again, the antenna loop is used to generate a magnetic field from which the RF signals are transmitted.
In another embodiment of the present invention, the RF transmitter may be directly coupled to the metallic plate without having a ground connection. The antenna system is comprised of the metallic plate. The metallic plate operates as a whip or dipole antenna that is used to generate an electric field from which RF signals are transmitted in accordance with electromagnetic propagation principles.
The present invention advantageously uses the metallic plate preexisting in many conventional keyboards as a part of the antenna system to increase the radiation efficiency of the antenna. Further, the present invention illustrates this increase in efficiency by providing good radiation characteristics in both horizontal polarization and vertical polarization. The increased efficiency of the present invention beneficially provides a wireless keyboard that consumes less power than conventional wireless keyboards. In one embodiment, the antenna system and apparatus uses only a 3.0 volt power supply, such as that provided by two 1.5-volt batteries, for example.
In addition to the increased efficiency and reduced power consumption, the present invention is also advantageously compact so that it can reside within the housing of the wireless keyboard. The present invention also provides for easy connection to the printed circuit board that includes the radio-frequency transmitter.
The features and advantages described in the specification are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter.